Adhesive for polarizing plate, polarizing plate, method for producing same, optical film and image display

ABSTRACT

An adhesive for polarizing plate used in order to provide a transparent protective film on at least one surface of a polarizer, comprising a crosslinking agent in the range of more than 30 parts by weight and 46 parts by weight or less relative to 100 parts by weight of a polyvinyl alcohol-based resin having an acetoacetyl group, is excellent in water resistance.

TECHNICAL FIELD

This invention relates to an adhesive for polarizing plate. Theinvention further relates to a polarizing plate using the adhesive forpolarizing plate and a fabrication method therefor. The polarizing platealone or an optical film obtained by laminating the polarizing plate canconstitute an image display such as a liquid crystal display, anorganic. EL display or PDP.

BACKGROUND ART

In a liquid crystal display, for example, it is indispensable to disposepolarizers on both sides of a glass substrate providing a surface of aliquid crystal panel according to an image formation scheme adopted inthe display. A polarizer is generally obtained in a procedure in which apolyvinyl alcohol-based film is dyed with a dichroic material such asiodine, thereafter, the film is crosslinked with a crosslinking agentand then, mono-axially stretched to thereby form a film. Since thepolarizer is fabricated by stretching, it is easy to shrink. Since apolyvinyl alcohol-based film comprises a hydrophilic polymer, the filmis very easily deformed especially in a humidified condition. Since thefilm itself is weak in mechanical strength, there has been a problemthat the film is torn. Hence, adopted is a reinforced polarizing platefabricated in a procedure in which a transparent protective film ortransparent protective films each made from triacetyl cellulose or thelike are adhered to on one side or both sides of a polarizer. Thepolarizing plate is fabricated by adhere the transparent protective filmonto a polarizer using an adhesive.

A liquid crystal display in recent years has broadened applications,which covers a wide range from a portable terminal to a home large-sizedTV, and sets of specifications have been provided for various kinds ofapplications. Especially, in the application of a portable terminal, auser as a precondition carries on while moving; therefore, the portableterminal has very severe requirements for durability. Therefore, apolarizing plate is required a durability that any of characteristics,and a shape does not change even in a humidified condition where dewdrops are formed.

A polarizer is, as described above, used as a polarizing plate obtainedby being reinforced with the transparent protective film. As adhesivesfor the polarizing plate conventionally used in adhesion of thetransparent protective film to the polarizer, preferable is an aqueousadhesive, for example a polyvinyl alcohol-based adhesive prepared bymixing a crosslinking agent into a polyvinyl alcohol aqueous solution. Apolyvinyl alcohol-based resin adhesive has had a case where thetransparent protective film is peeled at the interface between thepolarizer and the transparent protective film in a humidified condition.This is considered because the polyvinyl alcohol-based resin, which is amain component of the adhesive, is a water-soluble polymer andtherefore, there occurs a possibility that the adhesive dissolvesthereof in an environment of dewing.

In light of the problems, proposal has been made of an adhesive forpolarizing plate comprising a polyvinyl alcohol-based resin having anacetoacetyl group and a crosslinking agent (for example, Patent Document1). Even the adhesive for polarizer described in patent document 1,however, is insufficient in water resistance.

Patent Document 1: JP-A No. 7-198945.

DISCLOSURE OF INVENTION

It is an object of the invention to provide an adhesive for polarizingplate excellent in water resistance. It is another object of theinvention to provide a polarizing plate using the adhesive forpolarizing plate and a fabrication method therefor. It is still anotherobject of the invention to provide an optical film as a laminate of thepolarizing plate and it is a further object of the invention to providean image display such as a liquid crystal display.

The inventors have conducted serious studies in order to solve the abovetasks with findings that the objects can be achieved with an adhesivefor polarizing plate shown below, having led to completion of theinvention.

That is, the invention is related to an adhesive for polarizing plateused in order to provide a transparent protective film on at least onesurface of a polarizer,

-   -   comprising a crosslinking agent in the range of more than 30        parts by weight and 46 parts by weight or less relative to 100        parts by weight of a polyvinyl alcohol-based resin having an        acetoacetyl group.

Disclosed in Patent Document 1 is an adhesive prepared by mixing acrosslinking agent in the range of from 0.1 to 30 parts by weight into100 parts by weight of a polyvinyl alcohol-based resin having anacetoacetyl group. However, if a mixing content of the crosslinkingagent is 30 parts by weight or less, it cannot be said that there isobtained an adhesive having a sufficient water resistance in a dewingenvironment. It has been found that the adhesive for polarizing plate ofthe invention comprises a crosslinking agent in the range of more than30 parts by weight and 46 parts by weight or less relative to 100 partsby weight of a polyvinyl alcohol-based resin having an acetoacetyl groupand thereby, a water resistance thereof is drastically improved. Asample obtained by adhere a transparent protective film onto a polarizerwith an adhesive mixed with a crosslinking agent in the above range, asshown in the examples, is excellent in water resistance. That is, forexample, in a case where the sample is immersed in warm water of 60° C.for 5 hr in a durability test in a humidified condition, no peeling thatis visually recognizable was generated at an end portion of a polarizingplate even when 5 hr elapses in the immersion. On the other hand, when asample using an adhesive comprising a crosslinking agent at a contentless than 30 parts by weight was immersed in warm water of 60° C. for 1hr, shrinkage of a polarizer or decolorization of iodine developed at anend portion of the polarizing plate so as to be visually recognizable.

A mixing content of a crosslinking agent is in the range of more than 30parts by weight and 46 parts by weight or less relative to 100 parts byweight of a polyvinyl alcohol-based resin having an acetoacetyl group.The more a mixing content of a crosslinking agent is in the range, thebetter the agent works, wherein a mixing content thereof is preferably31 parts by weight or more, more preferably 32 parts by weight or moreand especially preferably 35 parts by weight or more. On the other hand,if a mixing content of a crosslinking agent is excessively more, areaction of a crosslinking agent progresses in a short time to therebytend to cause an adhesive to be gelated. As a result, a pot life as anadhesive is extremely shorter, which makes industrial use thereofdifficult. A mixing content of a crosslinking agent is preferably 46parts by weight or less, more preferably 45 parts by weight or less andmost preferably 40 parts by weight or less from the view point describedabove.

As a crosslinking agent used in the adhesive for polarizing plate,preferable comprises glyoxal and/or a compound having a methylol group.

The adhesive for polarizing plate is preferably used in a case where apolarizer is a polyvinyl alcohol-based polarizer and a transparentprotective film is a transparent protective cellulose-based film.

The invention is related to a polarizing plate in which a transparentprotective film is provided on at least one surface of a polarizer withan adhesive layer, wherein the adhesive layer is formed with the aboveadhesive for polarizing plate.

A thickness of an adhesive layer in the polarizing plate is in the rangeof from about 1 to 1000 nm, wherein if the thickness is excessivelylarger, unpreferably, it is hard to attain a uniform in-plane thicknessand a problem, which is generation of scale-like non-uniformity inthickness etc., arises in appearance with ease. Therefore, the thicknessis preferably 300 nm or less, more preferably 120 nm or less andespecially preferably 95 nm or less. In the invention, an effect ofimproving an adhesive strength and durability is exerted by increasing acontent of a crosslinking agent in the adhesive, whereas if thethickness is excessively thinner, an adhesive strength is insufficientin practical as polarizing plate. Hence, a thickness of the adhesivelayer is preferably 30 nm or more, more preferably 40 nm or more, andespecially preferably 50 nm or more. No specific limitation is placed ona method for adjusting a thickness of the adhesive layer, andexemplified is a method for adjusting a solid matter concentration of anadhesive solution or an operating condition of a coater for theadhesive. In a case of an adhesive of the invention comprising apolyvinyl alcohol-based resin having an acetoacetyl group, there arisesa tendency that a viscosity is lower than an adhesive comprising apolyvinyl alcohol-based resin that has been conventionally used;therefore, the adhesive to be obtained has a sufficient adhesivestrength even if a thickness of the adhesive layer is thin. No specificlimitation is placed on a measurement method for a thickness of anadhesive layer and preferable is used a sectional observation andmeasurement with SEM (Scanning Electron Microscopy).

The invention is related to a fabrication method for polarizing plate inwhich a transparent protective film is provided on at least one surfaceof a polarizer with an adhesive layer, comprising the steps of:

-   -   preparing the above adhesive for polarizing plate; coating the        adhesive for polarizing plate on a surface of the polarizer on        which the adhesive layer is formed and/or a surface of the        transparent protective film on which the adhesive layer is        formed; and adhering the transparent protective film and the        polarizer.

It is preferable that in the fabrication method for polarizing plate, atime taken until the adhesive for polarizing plate is coated after theadhesive for polarizer is prepared is preferably 240 min or less. Hence,an adhesive for polarizing plate is preferably prepared by mixing acrosslinking agent in the range of more than 30 parts by weight and 46parts by weight or less into 100 parts by weight of a polyvinylalcohol-based resin having an acetoacetyl group within 240 min prior toconducting of a coating step.

There arises a tendency that an adhesive prepared by mixing acrosslinking agent into a polyvinyl alcohol-based resin having anacetoacetyl group is gelated if the adhesive is left as it is for a longtime. Hence, preparation of the adhesive is preferably completed in theshortest possible time prior to the coating. A preparation of theadhesive is conducted preferably within 240 min, more preferably within180 min, further more preferably within 90 min, still further morepreferably within 45 min and especially preferably within 30 min, priorto coating the adhesive.

It is preferable that in the fabrication method for polarizing plate,the preparation step for the adhesive for polarizing plate, the coatingstep for the adhesive for polarizing plate and the adhesion step ofadhering the transparent protective film and the polarizer are allconducted at a temperature in the state of 25 to 50° C.

In connection with the adhesive, preferably controlled are temperatures,respectively, in the steps from preparation of the adhesive by mixing acrosslingking agent into a polyvinyl alcohol-based resin having anacetoacetyl group to coating thereof, and the adhesion step. Such acontrol of a temperature of an adhesive can improve a water resistance.A control temperature of the adhesive is preferably in the range of from25 to 50° C., more preferably in the range of from 30 to 45° C. andfurther more preferably in the range of from 30 to 40° C. If thetemperature is lower than 25° C., a water resistance is poor and peelingeasily occurs between protective film and polarizer in a humidifiedcondition. If the temperature is higher than 50° C., an adhesive iseasily gelated immediately after mixing a crosslinking agent, whichrenders the adhesive difficult in use.

The invention is related to an optical film comprising at least oneabove polarizing plate.

The invention is related to an image display comprising the abovepolarizing plate or the above optical film.

BEST MODE FOR CARRYING OUT THE INVENTION

An adhesive for polarizing plate of the invention comprises acrosslinking agent and a polyvinyl alcohol-based resin having anacetoacetyl group.

A polyvinyl alcohol-based resin having an acetoacetyl group is obtainedby reacting a polyvinyl alcohol-based resin and diketene to each otherwith a known method. Examples of known methods include: a method inwhich a polyvinyl alcohol-based resin is dispersed into a solvent suchas acetic acid, to which diketene is added and a method in which apolyvinyl alcohol-based resin is previously dissolved into a solventsuch as dimethylformamide or dioxane, to which diketene is added.Another example is a method in which diketene gas or diketene liquid isbrought into direct contact with a polyvinyl alcohol.

Examples of polyvinyl alcohol-based resin include: a polyvinyl alcoholobtained by saponifying a polyvinyl acetate; a derivative thereof; asaponified copolymer of vinyl acetate and a monomer copolymerizabletherewith; and polyvinyl alcohols modified by acetalization,urethanization, etherification, grafting, phosphate esterification andthe like. Examples of the monomers include, unsaturated carboxylic acidssuch as maleic anhydride, fumaric acid, crotonic acid, itaconic acid and(meth) acrylic acid, and esters thereof; α-olefins such as ethylene andpropylene; (meth)allylsulfonic acid or sodium salt thereof,(meth)allylsulfonate; sodium sulfonate (monoalkyl maleate), sodiumdisulfonate (alkyl maleate); N-methylolacrylamide; an alkai salt ofacrylamide alkylsulfonate; N-vinylpyrrolidone, a derivative ofN-vinylpyrrolidone and the like. The polyvinyl alcohol-based resins canbe either used alone or in combination of two kinds or more.

While no specific limitation is imposed on a polyvinyl alcohol-basedresin, an average degree of polymerization is from about 100 to about3000, preferably from 500 to 3000 and an average degree ofsaponification is from about 85 to about 100 mol %, preferably from 90to 100 mol % in consideration of adherence.

No specific limitation is imposed on a degree of modification by anacetoacetyl group in a polyvinyl alcohol-based resin having anacetoacetyl group or groups as far as the degree of modification is 0.1mol % or more. If the degree of modification is less than 0.1 mol %,water resistance of an adhesive layer is insufficient, which isimproper. A degree of modification by an acetoacetyl group is preferablyfrom about 0.1 to about 40 mol %, more preferably from 2 to 7 mol %. Ifa degree of modification by an acetoacetyl group exceeds 40 mol %,reaction sites with a crosslinking agent is fewer to thereby reduce aneffect of improvement on water resistance.

Any of crosslinking agents that have been used in a polyvinylalcohol-based adhesive can be used as a crosslinking agent in theinvention without a specific limitation thereon. A crosslinking agentthat can be used is a compound having at least two functional groupshaving reactivity with a polyvinyl alcohol-based resin. Examples thereofinclude: alkylene diamines having an alkylene group and two amino groupssuch as ethylene diamine, triethylene diamine and hexamethylene diamine;isocyanates such as tolylene diisocyanate, hydrogenated tolylenediisocyanate, trimethylolpropane tolylene diisocyanate adduct,triphenylmethane triisocyanate, methylenebis(4-phenylmethane)triisocyanate and isophorone diisocyanate, and ketoxime-blocked productsthereof or isocyanates of phenol-blocked products; epoxy compounds suchas ethylene glycol diglycidyl ether, polyethylene glycol diglycidylether, glycerin di- or triglycidyl ether, 1,6-hexanediol diglycidylether, trimethylolpropane triglycidyl ether, diglicidyl aniline anddiglycidyl amine; monoaldehydes such as formaldehyde, acetaldehyde,propionaldehyde and butylaldehyde; dialdehydes such as glyoxal,malonaldehyde, succindialdehyde, glutardialdehyde, maleic dialdehyde andphthaldialdehyde; amino-formaldehyde resins such as condensates withformaldehyde of methylolurea, methylolmelamine, alkylated methylolurea,alkylated methylolmelamine, acetoguanamine and benzoguanamine; salts ofdivalent metals or trivalent metals such as sodium, potassium,magnesium, calcium, aluminum, iron and nickel, and oxides of the metals.Preferable among the crosslinking agents are amino-formaldehyde resinsand dialdehydes. As amino-formaldehyde resins, preferable is a compoundhaving a methylol group and as dialdehydes, preferable is glyoxal.Preferable is a compound having a methylol group, especially preferableis a methylolmelamine.

A crosslinking agent in the range of more than 30 parts by weight and 46parts by weight or less is, as described above, mixed into 100 parts byweight of a polyvinyl alcohol-based resin having an acetoacetyl group.

An adhesive for polarizing plate comprising a crosslinking agent and apolyvinyl alcohol-based resin having an acetoacetyl group is usuallyused as an aqueous solution. No specific limitation is imposed on aconcentration thereof in the aqueous solution, and the concentration isusually from 0.1 to 15 wt % and preferably from 0.5 to 10 wt % inconsideration of coatability and self stability etc.

Note that various additives described below can be further mixed into anadhesive: coupling agents such as a silane coupling agent and a titaniumcoupling agent; various kinds of tackifiers; an ultraviolet absorbent;an antioxidant; stabilizers such as a heat resistance stabilizer and ahydrolysis resistance stabilizer; and the like.

A polarizing plate of the invention is fabricated by adhere atransparent protective film to a polarizer with the adhesive. Atransparent protective film or transparent protective films are providedon one surface or both surfaces of a polarizer with an adhesive agentlayer formed with the adhesive for polarizing plate interposedtherebetween.

Coating with the adhesive may be performed on any or both of thetransparent protective film and the polarizer. Coating with the adhesiveis preferably performed so that a thickness of a coat after drying is inthe range of from 1 to 1000 nm. No specific limitation is imposed on acoating operation and there can be adopted any of methods including aroller coating method, a spray coating, a dipping method and others.

Preparation of the adhesive is, as described above, preferably completedwithin 4 hr prior to coating of the adhesive. A process from preparationof the adhesive to coating thereof within a time as short as 4 hr can berealized by incorporating a preparation step for the adhesive as partinto a fabrication process for a polarizer including a series of steps,or alternatively, by disposing a proper preparation apparatus.

After the adhesive is coated, the transparent protective is adhered tothe polarizer with a roll laminator or the like. After adhesion, adrying step is performed to thereby form an adhesive layer that is a drycoated layer. A drying temperature is from about 5 to about 150° C.preferably from 30 to 120° C. and for a time of 120 sec or longer,preferably for a time 300 sec or longer.

Temperatures are preferably controlled in the preparation step, thecoating step and the adhesion step, respectively. Control of atemperature of an adhesive can improve a water resistance. A controltemperature of an adhesive is preferably in the range of from 25 to 50°C., as described above.

A polarizer is not limited especially but various kinds of polarizer maybe used. As a polarizer, for example, a film that is uniaxiallystretched after having dichromatic substances, such as iodine anddichromatic dye, absorbed to hydrophilic high molecular weight polymerfilms, such as polyvinyl alcohol type film, partially formalizedpolyvinyl alcohol type film, and ethylene-vinyl acetate copolymer typepartially saponified film; poly-ene type orientation films, such asdehydrated polyvinyl alcohol and dehydrochlorinated polyvinyl chloride,etc. may be mentioned. In these, a polyvinyl alcohol type film comprisesdichromatic materials such as iodine is suitably used. Althoughthickness of polarizer is not especially limited, the thickness of about5 to 80 μm is commonly adopted.

A polarizer that is uniaxially stretched after a polyvinyl alcohol typefilm dyed with iodine is obtained by stretching a polyvinyl alcohol filmby 3 to 7 times the original length, after dipped and dyed in aqueoussolution of iodine. If needed the film may also be dipped in aqueoussolutions, such as boric acid and potassium iodide. Furthermore, beforedyeing, the polyvinyl alcohol type film may be dipped in water andrinsed if needed. By rinsing polyvinyl alcohol type film with water,effect of preventing un-uniformity, such as unevenness of dyeing, isexpected by making polyvinyl alcohol type film swelled in addition thatalso soils and blocking inhibitors on the polyvinyl alcohol type filmsurface may be washed off. Stretching may be applied after dyed withiodine or may be applied concurrently, or conversely dyeing with iodinemay be applied after stretching. Stretching is applicable in aqueoussolutions, such as boric acid and potassium iodide, and in water bath.

Proper transparent materials may be used as a transparent polymer or afilm material that forms the transparent protective file, and thematerial having outstanding transparency, mechanical strength, heatstability and outstanding moisture interception property, etc. may bepreferably used. As materials of the above-mentioned transparentprotective film, for example, polyester type polymers, such aspolyethylene terephthalate and polyethylenenaphthalate; cellulose typepolymers, such as diacetyl cellulose and triacetyl cellulose; acrylicstype polymer, such as poly methylmethacrylate; styrene type polymers,such as polystyrene and acrylonitrile-styrene copolymer (AS resin);polycarbonate type polymer may be mentioned. Besides, as examples of thepolymer forming a transparent protective film, polyolefin type polymers,such as polyethylene, polypropylene, polyolefin that has cyclo-type ornorbornene structure, ethylene-propylene copolymer; vinyl chloride typepolymer; amide type polymers, such as nylon and aromatic polyamide;imide type polymers; sulfone type polymers; polyether sulfone typepolymers; polyether-ether ketone type polymers; poly phenylene sulfidetype polymers; vinyl alcohol type polymer; vinylidene chloride typepolymers; vinyl butyral type polymers; allylate type polymers;polyoxymethylene type polymers; epoxy type polymers; or blend polymersof the above-mentioned polymers may be mentioned. The transparentprotective film is formed as a cured layer made of heat curing type orultraviolet ray curing type resins, such as acryl based, urethane based,acryl urethane based, epoxy based, and silicone based, etc.

Moreover, as is described in Japanese Patent Laid-Open Publication No.2001-343529 (WO 01/37007), polymer films, for example, resincompositions including (A) thermoplastic resins having substitutedand/or non-substituted imido group is in side chain, and (B)thermoplastic resins having substituted and/or non-substituted phenyland nitrile group in sidechain may be mentioned. As an illustrativeexample, a film may be mentioned that is made of a resin compositionincluding alternating copolymer comprising iso-butylene and N-methylmaleimide, and acrylonitrile-styrene copolymer. A film comprisingmixture extruded article of resin compositions etc. may be used. Sincethe films are less in retardation and less in photoelastic coefficient,faults such as unevenness due to a strain in a polarizing plate can beremoved and besides, since they are less in moisture permeability, theyare excellent in durability under humidified environment.

Thickness values of the transparent protective film can be properlydetermined and generally on the order in the range of from about 1 toabout 500 μm from the viewpoint of a strength, workability such ashandlability, requirement for a thin film and the like. Especially, thethickness values are preferably is in the range of from 1 to 300 μm andmore preferably in the range of from 5 to 200 μm.

Moreover, it is preferable that the transparent protection film may haveas little coloring as possible. Accordingly, a protection film having aretardation value in a film thickness direction represented byRth=[(nx+ny)/2−nz]×d of from −90 nm to +75 nm (where, nx and nyrepresent principal indices of refraction in a film plane, nz representsrefractive index in a film thickness direction, and d represents a filmthickness) may be preferably used. Thus, coloring (optical coloring) ofpolarizing plate resulting from a protection film may mostly becancelled using a protection film having a retardation value (Rth) offrom −90 nm to +75 nm in a thickness direction. The retardation value(Rth) in a thickness direction is preferably from −80 nm to +60 nm, andespecially preferably from −70 nm to +45 nm.

As transparent protective films, preferable are a cellulose-basedpolymer such as triacetyl cellulose from the standpoint of apolarization characteristic, a durability or the like. Especiallypreferable is a triacetyl cellulose film. Note that in a case whereprotective films are provided on both sides of a polarizer, theprotective films made from the same polymer may be used on both sidesthereof or alternatively, the protective films made from polymermaterials different from each other may also be used on respective bothsides thereof.

An easy adhesion treatment can be applied onto a surface of atransparent protective film which is adhered to a polarizer. Examples ofeasy adhesion treatments include: dry treatments such as a plasmatreatment and a corona treatment; chemical treatment such as alkalinetreatment (saponification treatment); and a coating treatment in whichan easy adhesion layer is formed. Among them, preferable are a coatingtreatment and an alkaline treatment each forming an easy adhesion layer.In formation of an easy adhesion layer, there can be used each ofvarious kinds of easy adhesion materials such as a polyol resin, apolycarboxylic resin and a polyester resin. Note that a thickness of aneasy adhesion layer is preferably usually from about 0.01 to about 10μm, more preferably from about 0.05 to about 5 μm and especiallypreferably from about 0.1 to about 1 μm.

A hard coat layer may be prepared, or antireflection processing,processing aiming at sticking prevention, diffusion or anti glare may beperformed onto the face on which the polarizing film of the abovedescribed transparent protective film has not been adhered.

A hard coat processing is applied for the purpose of protecting thesurface of the polarizing plate from damage, and this hard coat film maybe formed by a method in which, for example, a curable coated film withexcellent hardness, slide property etc. is added on the surface of theprotective film using suitable ultraviolet curable type resins, such asacrylic type and silicone type resins. Antireflection processing isapplied for the purpose of antireflection of outdoor daylight on thesurface of a polarizing plate and it may be prepared by forming anantireflection film according to the conventional method etc. Besides, asticking prevention processing is applied for the purpose of adherenceprevention with adjoining layer.

In addition, an anti glare processing is applied in order to prevent adisadvantage that outdoor daylight reflects on the surface of apolarizing plate to disturb visual recognition of transmitting lightthrough the polarizing plate, and the processing may be applied, forexample, by giving a fine concavo-convex structure to a surface of theprotective film using, for example, a suitable method, such as roughsurfacing treatment method by sandblasting or embossing and a method ofcombining transparent fine particle. As a fine particle combined inorder to form a fine concavo-convex structure on the above-mentionedsurface, transparent fine particles whose average particle size is 0.5to 50 μm, for example, such as inorganic type fine particles that mayhave conductivity comprising silica, alumina, titania, zirconia, tinoxides, indium oxides, cadmium oxides, antimony oxides, etc., andorganic type fine particles comprising cross-linked of non-cross-linkedpolymers may be used. When forming fine concavo-convex structure on thesurface, the amount of fine particle used is usually about 2 to 50weight parts to the transparent resin 100 weight parts that forms thefine concavo-convex structure on the surface, and preferably 5 to 25weight parts. An anti glare layer may serve as a diffusion layer(viewing angle expanding function etc.) for diffusing transmitting lightthrough the polarizing plate and expanding a viewing angle etc.

In addition, the above-mentioned antireflection layer, stickingprevention layer, diffusion layer, anti glare layer, etc. may be builtin the protective film itself, and also they may be prepared as anoptical layer different from the protective film.

A polarizing plate of the present invention may be used in practical useas an optical film laminated with other optical layers. Although thereis especially no limitation about the optical layers, one layer or twolayers or more of optical layers, which may be used for formation of aliquid crystal display etc., such as a reflector, a transreflectiveplate, a retardation plate (a half wavelength plate and a quarterwavelength plate included), and a viewing angle compensation film, maybe used. Especially preferable polarizing plates are; a reflection typepolarizing plate or a transreflective type polarizing plate in which areflector or a transreflective reflector is further laminated onto apolarizing plate of the present invention; an elliptically polarizingplate or a circular polarizing plate in which a retardation plate isfurther laminated onto the polarizing plate; a wide viewing anglepolarizing plate in which a viewing angle compensation film is furtherlaminated onto the polarizing plate; or a polarizing plate in which abrightness enhancement film is further laminated onto the polarizingplate.

A reflective layer is prepared on a polarizing plate to give areflection type polarizing plate, and this type of plate is used for aliquid crystal display in which an incident light from a view side(display side) is reflected to give a display. This type of plate doesnot require built-in light sources, such as a backlight, but has anadvantage that a liquid crystal display may easily be made thinner. Areflection type polarizing plate may be formed using suitable methods,such as a method in which a reflective layer of metal etc. is, ifrequired, attached to one side of a polarizing plate through atransparent protective film etc.

As an example of a reflection type polarizing plate, a plate may bementioned on which, if required, a reflective layer is formed using amethod of attaching a foil and vapor deposition film of reflectivemetals, such as aluminum, to one side of a matte treated protectivefilm. Moreover, a different type of plate with a fine concavo-convexstructure on the surface obtained by mixing fine particle into theabove-mentioned protective film, on which a reflective layer ofconcavo-convex structure is prepared, may be mentioned. The reflectivelayer that has the above-mentioned fine concavo-convex structurediffuses incident light by random reflection to prevent directivity andglaring appearance, and has an advantage of controlling unevenness oflight and darkness etc. Moreover, the protective film containing thefine particle has an advantage that unevenness of light and darkness maybe controlled more effectively, as a result that an incident light andits reflected light that is transmitted through the film are diffused. Areflective layer with fine concavo-convex structure on the surfaceeffected by a surface fine concavo-convex structure of a protective filmmay be formed by a method of attaching a metal to the surface of atransparent protective film directly using, for example, suitablemethods of a vacuum evaporation method, such as a vacuum depositionmethod, an ion plating method, and a sputtering method, and a platingmethod etc.

Instead of a method in which a reflection plate is directly given to theprotective film of the above-mentioned polarizing plate, a reflectionplate may also be used as a reflective sheet constituted by preparing areflective layer on the suitable film for the transparent film. Inaddition, since a reflective layer is usually made of metal, it isdesirable that the reflective side is covered with a protective film ora polarizing plate etc. when used, from a viewpoint of preventingdeterioration in reflectance by oxidation, of maintaining an initialreflectance for a long period of time and of avoiding preparation of aprotective layer separately etc.

In addition, a transreflective type polarizing plate may be obtained bypreparing the above-mentioned reflective layer as a transreflective typereflective layer, such as a half-mirror etc. that reflects and transmitslight. A transreflective type polarizing plate is usually prepared inthe backside of a liquid crystal cell and it may form a liquid crystaldisplay unit of a type in which a picture is displayed by an incidentlight reflected from a view side (display side) when used in acomparatively well-lighted atmosphere. And this unit displays a picture,in a comparatively dark atmosphere, using embedded type light sources,such as a back light built in backside of a transreflective typepolarizing plate. That is, the transreflective type polarizing plate isuseful to obtain of a liquid crystal display of the type that savesenergy of light sources, such as a back light, in a well-lightedatmosphere, and can be used with a built-in light source if needed in acomparatively dark atmosphere etc.

The above-mentioned polarizing plate may be used as ellipticallypolarizing plate or circularly polarizing plate on which the retardationplate is laminated. A description of the above-mentioned ellipticallypolarizing plate or circularly polarizing plate will be made in thefollowing paragraph. These polarizing plates change linearly polarizedlight into elliptically polarized light or circularly polarized light,elliptically polarized light or circularly polarized light into linearlypolarized light or change the polarization direction of linearlypolarization by a function of the retardation plate. As a retardationplate that changes circularly polarized light into linearly polarizedlight or linearly polarized light into circularly polarized light, whatis called a quarter wavelength plate (also called λ/4 plate) is used.Usually, half-wavelength plate (also called λ/2 plate) is used, whenchanging the polarization direction of linearly polarized light.

Elliptically polarizing plate is effectively used to give a monochromedisplay without above-mentioned coloring by compensating (preventing)coloring (blue or yellow color) produced by birefringence of a liquidcrystal layer of a super twisted nematic (STN) type liquid crystaldisplay. Furthermore, a polarizing plate in which three-dimensionalrefractive index is controlled may also preferably compensate (prevent)coloring produced when a screen of a liquid crystal display is viewedfrom an oblique direction. Circularly polarizing plate is effectivelyused, for example, when adjusting a color tone of a picture of areflection type liquid crystal display that provides a colored picture,and it also has function of antireflection. For example, a retardationplate may be used that compensates coloring and viewing angle, etc.caused by birefringence of various wavelength plates or liquid crystallayers etc. Besides, optical characteristics, such as retardation, maybe controlled using laminated layer with two or more sorts ofretardation plates having suitable retardation value according to eachpurpose. As retardation plates, birefringence films formed by stretchingfilms comprising suitable polymers, such as polycarbonates, norbornenetype resins, polyvinyl alcohols, polystyrenes, poly methylmethacrylates, polypropylene; polyallylates and polyamides; alignedfilms comprising liquid crystal materials, such as liquid crystalpolymer; and films on which an alignment layer of a liquid crystalmaterial is supported may be mentioned. A retardation plate may be aretardation plate that has a proper retardation according to thepurposes of use, such as various kinds of wavelength plates and platesaiming at compensation of coloring by birefringence of a liquid crystallayer and of visual angle, etc., and may be a retardation plate in whichtwo or more sorts of retardation plates is laminated so that opticalproperties, such as retardation, may be controlled.

The above-mentioned elliptically polarizing plate and an above-mentionedreflected type elliptically polarizing plate are laminated platecombining suitably a polarizing plate or a reflection type polarizingplate with a retardation plate. This type of elliptically polarizingplate etc. may be manufactured by combining a polarizing plate(reflected type) and a retardation plate, and by laminating them one byone separately in the manufacture process of a liquid crystal display.On the other hand, the polarizing plate in which lamination wasbeforehand carried out and was obtained as an optical film, such as anelliptically polarizing plate, is excellent in a stable quality, aworkability in lamination etc., and has an advantage in improvedmanufacturing efficiency of a liquid crystal display.

A viewing angle compensation film is a film for extending viewing angleso that a picture may look comparatively clearly, even when it is viewedfrom an oblique direction not from vertical direction to a screen. Assuch a viewing angle compensation retardation plate, in addition, a filmhaving birefringence property that is processed by uniaxial stretchingor orthogonal biaxial stretching and a biaxial stretched film asinclined alignment film etc. may be used. As inclined alignment film,for example, a film obtained using a method in which a heat shrinkingfilm is adhered to a polymer film, and then the combined film is heatedand stretched or shrinked under a condition of being influenced by ashrinking force, or a film that is aligned in oblique direction may bementioned. The viewing angle compensation film is suitably combined forthe purpose of prevention of coloring caused by change of visible anglebased on retardation by liquid crystal cell etc. and of expansion ofviewing angle with good visibility.

Besides, a compensation plate in which an optical anisotropy layerconsisting of an alignment layer of liquid crystal polymer, especiallyconsisting of an inclined alignment layer of discotic liquid crystalpolymer is supported with triacetyl cellulose film may preferably beused from a viewpoint of attaining a wide viewing angle with goodvisibility.

The polarizing plate with which a polarizing plate and a brightnessenhancement film are adhered together is usually used being prepared ina backside of a liquid crystal cell. A brightness enhancement film showsa characteristic that reflects linearly polarized light with apredetermined polarization axis, or circularly polarized light with apredetermined direction, and that transmits other light, when naturallight by back lights of a liquid crystal display or by reflection from aback-side etc., comes in. The polarizing plate, which is obtained bylaminating a brightness enhancement film to a polarizing plate, thusdoes not transmit light without the predetermined polarization state andreflects it, while obtaining transmitted light with the predeterminedpolarization state by accepting a light from light sources, such as abacklight. This polarizing plate makes the light reflected by thebrightness enhancement film further reversed through the reflectivelayer prepared in the backside and forces the light re-enter into thebrightness enhancement film, and increases the quantity of thetransmitted light through the brightness enhancement film bytransmitting a part or all of the light as light with the predeterminedpolarization state. The polarizing plate simultaneously suppliespolarized light that is difficult to be absorbed in a polarizer, andincreases the quantity of the light usable for a liquid crystal picturedisplay etc., and as a result luminosity may be improved. That is, inthe case where the light enters through a polarizer from backside of aliquid crystal cell by the back light etc. without using a brightnessenhancement film, most of the light, with a polarization directiondifferent from the polarization axis of a polarizer, is absorbed by thepolarizer, and does not transmit through the polarizer. This means thatalthough influenced with the characteristics of the polarizer used,about 50 percent of light is absorbed by the polarizer, the quantity ofthe light usable for a liquid crystal picture display etc. decreases somuch, and a resulting picture displayed becomes dark. A brightnessenhancement film does not enter the light with the polarizing directionabsorbed by the polarizer into the polarizer but reflects the light onceby the brightness enhancement film, and further makes the light reversedthrough the reflective layer etc. prepared in the backside to re-enterthe light into the brightness enhancement film. By this above-mentionedrepeated operation, only when the polarization direction of the lightreflected and reversed between the both becomes to have the polarizationdirection which may pass a polarizer, the brightness enhancement filmtransmits the light to supply it to the polarizer. As a result, thelight from a backlight may be efficiently used for the display of thepicture of a liquid crystal display to obtain a bright screen.

A diffusion plate may also be prepared between brightness enhancementfilm and the above described reflective layer, etc. A polarized lightreflected by the brightness enhancement film goes to the above describedreflective layer etc., and the diffusion plate installed diffusespassing light uniformly and changes the light state into depolarizationat the same time. That is, the diffusion plate returns polarized lightto natural light state. Steps are repeated where light, in theunpolarized state, i.e., natural light state, reflects throughreflective layer and the like, and again goes into brightnessenhancement film through diffusion plate toward reflective layer and thelike. Diffusion plate that returns polarized light to the natural lightstate is installed between brightness enhancement film and the abovedescribed reflective layer, and the like, in this way, and thus auniform and bright screen may be provided while maintaining brightnessof display screen, and simultaneously controlling non-uniformity ofbrightness of the display screen. By preparing such diffusion plate, itis considered that number of repetition times of reflection of a firstincident light increases with sufficient degree to provide uniform andbright display screen conjointly with diffusion function of thediffusion plate.

The suitable films are used as the above-mentioned brightnessenhancement film. Namely, multilayer thin film of a dielectricsubstance; a laminated film that has the characteristics of transmittinga linearly polarized light with a predetermined polarizing axis, and ofreflecting other light, such as the multilayer laminated film of thethin film having a different refractive-index anisotropy; an alignedfilm of cholesteric liquid-crystal polymer; a film that has thecharacteristics of reflecting a circularly polarized light with eitherleft-handed or right-handed rotation and transmitting other light, suchas a film on which the aligned cholesteric liquid crystal layer issupported; etc. may be mentioned.

Therefore, in the brightness enhancement film of a type that transmits alinearly polarized light having the above-mentioned predeterminedpolarization axis, by arranging the polarization axis of the transmittedlight and entering the light into a polarizing plate as it is, theabsorption loss by the polarizing plate is controlled and the polarizedlight can be transmitted efficiently. On the other hand, in thebrightness enhancement film of a type that transmits a circularlypolarized light as a cholesteric liquid-crystal layer, the light may beentered into a polarizer as it is, but it is desirable to enter thelight into a polarizer after changing the circularly polarized light toa linearly polarized light through a retardation plate, taking controlan absorption loss into consideration. In addition, a circularlypolarized light is convertible into a linearly polarized light using aquarter wavelength plate as the retardation plate.

A retardation plate that works as a quarter wavelength plate in a widewavelength ranges, such as a visible-light band, is obtained by a methodin which a retardation layer working as a quarter wavelength plate to apale color light with a wavelength of 550 nm is laminated with aretardation layer having other retardation characteristics, such as aretardation layer working as a half-wavelength plate. Therefore, theretardation plate located between a polarizing plate and a brightnessenhancement film may consist of one or more retardation layers.

In addition, also in a cholesteric liquid-crystal layer, a layerreflecting a circularly polarized light in a wide wavelength ranges,such as a visible-light band, may be obtained by adopting aconfiguration structure in which two or more layers with differentreflective wavelength are laminated together. Thus a transmittedcircularly polarized light in a wide wavelength range may be obtainedusing this type of cholesteric liquid-crystal layer.

Moreover, the polarizing plate may consist of multi-layered film oflaminated layers of a polarizing plate and two of more of optical layersas the above-mentioned separated type polarizing plate. Therefore, apolarizing plate may be a reflection type elliptically polarizing plateor a semi-transmission type elliptically polarizing plate, etc. in whichthe above-mentioned reflection type polarizing plate or atransreflective type polarizing plate is combined with above describedretardation plate respectively.

Although an optical film with the above described optical layerlaminated to the polarizing plate may be formed by a method in whichlaminating is separately carried out sequentially in manufacturingprocess of a liquid crystal display etc., an optical film in a form ofbeing laminated beforehand has an outstanding advantage that it hasexcellent stability in quality and assembly workability, etc., and thusmanufacturing processes ability of a liquid crystal display etc. may beraised. Proper adhesion means, such as an adhesive layer, may be usedfor laminating. On the occasion of adhesion of the above describedpolarizing plate and other optical films, the optical axis may be set asa suitable configuration angle according to the target retardationcharacteristics etc.

In the polarizing plate mentioned above and the optical film in which atleast one layer of the polarizing plate is laminated, an adhesive layermay also be prepared for adhesion with other members, such as a liquidcrystal cell etc. As pressure sensitive adhesive that forms adhesivelayer is not especially limited, and, for example, acrylic typepolymers; silicone type polymers; polyesters, polyurethanes, polyamides,polyethers; fluorine type and rubber type polymers may be suitablyselected as a base polymer. Especially, a pressure sensitive adhesivesuch as acrylics type pressure sensitive adhesives may be preferablyused, which is excellent in optical transparency, showing adhesioncharacteristics with moderate wettability, cohesiveness and adhesiveproperty and has outstanding weather resistance, heat resistance, etc.

Moreover, an adhesive layer with low moisture absorption and excellentheat resistance is desirable. This is because those characteristics arerequired in order to prevent foaming and peeling-off phenomena bymoisture absorption, in order to prevent decrease in opticalcharacteristics and curvature of a liquid crystal cell caused by thermalexpansion difference etc. and in order to manufacture a liquid crystaldisplay excellent in durability with high quality.

The adhesive layer may contain additives, for example, such as naturalor synthetic resins, adhesive resins, glass fibers, glass beads, metalpowder, fillers comprising other inorganic powder etc., pigments,colorants and antioxidants. Moreover, it may be an adhesive layer thatcontains fine particle and shows optical diffusion nature.

Proper method may be carried out to attach an adhesive layer to one sideor both sides of the optical film. As an example, about 10 to 40 weight% of the pressure sensitive adhesive solution in which a base polymer orits composition is dissolved or dispersed, for example, toluene or ethylacetate or a mixed solvent of these two solvents is prepared. A methodin which this solution is directly applied on a polarizing plate top oran optical film top using suitable developing methods, such as flowmethod and coating method, or a method in which an adhesive layer isonce formed on a separator, as mentioned above, and is then transferredon a polarizing plate or an optical film may be mentioned.

An adhesive layer may also be prepared on one side or both sides of apolarizing plate or an optical film as a layer in which pressuresensitive adhesives with different composition or different kind etc.are laminated together. Moreover, when adhesive layers are prepared onboth sides, adhesive layers that have different compositions, differentkinds or thickness, etc. may also be used on front side and backside ofa polarizing plate or an optical film. Thickness of an adhesive layermay be suitably determined depending on a purpose of usage or adhesivestrength, etc., and generally is 1 to 500 μm, preferably 5 to 200 μm,and more preferably 10 to 100 μm.

A temporary separator is attached to an exposed side of an adhesivelayer to prevent contamination etc., until it is practically used.Thereby, it can be prevented that foreign matter contacts adhesive layerin usual handling. As a separator, without taking the above-mentionedthickness conditions into consideration, for example, suitableconventional sheet materials that is coated, if necessary, with releaseagents, such as silicone type, long chain alkyl type, fluorine typerelease agents, and molybdenum sulfide may be used. As a suitable sheetmaterial, plastics films, rubber sheets, papers, cloths, no wovenfabrics, nets, foamed sheets and metallic foils or laminated sheetsthereof may be used.

In addition, in the present invention, ultraviolet absorbing propertymay be given to the above-mentioned each layer, such as a polarizer fora polarizing plate, a transparent protective film and an optical filmetc. and an adhesive layer, using a method of adding UV absorbents, suchas salicylic acid ester type compounds, benzophenol type compounds,benzotriazol type compounds, cyano acrylate type compounds, and nickelcomplex salt type compounds.

An optical film of the present invention may be preferably used formanufacturing various equipment, such as liquid crystal display, etc.Assembling of a liquid crystal display may be carried out according toconventional methods. That is, a liquid crystal display is generallymanufactured by suitably assembling several parts such as a liquidcrystal cell, optical films and, if necessity, lighting system, and byincorporating driving circuit. In the present invention, except that anoptical film by the present invention is used, there is especially nolimitation to use any conventional methods. Also any liquid crystal cellof arbitrary type, such as TN type, and STN type, π type may be used.

Suitable liquid crystal displays, such as liquid crystal display withwhich the above-mentioned optical film has been located at one side orboth sides of the liquid crystal cell, and with which a backlight or areflector is used for a lighting system may be manufactured. In thiscase, the optical film by the present invention may be installed in oneside or both sides of the liquid crystal cell. When installing theoptical films in both sides, they may be of the same type or ofdifferent type. Furthermore, in assembling a liquid crystal display,suitable parts, such as diffusion plate, anti-glare layer,antireflection film, protective plate, prism array, lens array sheet,optical diffusion plate, and backlight, may be installed in suitableposition in one layer or two or more layers.

Subsequently, organic electro luminescence equipment (organic ELdisplay) will be explained. Generally, in organic EL display, atransparent electrode, an organic emitting layer and a metal electrodeare laminated on a transparent substrate in an order configuring anilluminant (organic electro luminescence illuminant). Here, an organicemitting layer is a laminated material of various organic thin films,and much compositions with various combination are known, for example, alaminated material of hole injection layer comprising triphenylaminederivatives etc., a luminescence layer comprising fluorescent organicsolids, such as anthracene; a laminated material of electronic injectionlayer comprising such a luminescence layer and perylene derivatives,etc.; laminated material of these hole injection layers, luminescencelayer, and electronic injection layer etc.

An organic EL display emits light based on a principle that positivehole and electron are injected into an organic emitting layer byimpressing voltage between a transparent electrode and a metalelectrode, the energy produced by recombination of these positive holesand electrons excites fluorescent substance, and subsequently light isemitted when excited fluorescent substance returns to ground state. Amechanism called recombination which takes place in a intermediateprocess is the same as a mechanism in common diodes, and, as isexpected, there is a strong non-linear relationship between electriccurrent and luminescence strength accompanied by rectification nature toapplied voltage.

In an organic EL display, in order to take out luminescence in anorganic emitting layer, at least one electrode must be transparent. Thetransparent electrode usually formed with transparent electricconductor, such as indium tin oxide (ITO), is used as an anode. On theother hand, in order to make electronic injection easier and to increaseluminescence efficiency, it is important that a substance with smallwork function is used for cathode, and metal electrodes, such as Mg—Agand Al—Li, are usually used.

In organic EL display of such a configuration, an organic emitting layeris formed by a very thin film about 10 nm in thickness. For this reason,light is transmitted nearly completely through organic emitting layer asthrough transparent electrode. Consequently, since the light thatenters, when light is not emitted, as incident light from a surface of atransparent substrate and is transmitted through a transparent electrodeand an organic emitting layer and then is reflected by a metalelectrode, appears in front surface side of the transparent substrateagain, a display side of the organic EL display looks like mirror ifviewed from outside.

In an organic EL display containing an organic electro luminescenceilluminant equipped with a transparent electrode on a surface side of anorganic emitting layer that emits light by impression of voltage, and atthe same time equipped with a metal electrode on a back side of organicemitting layer, a retardation plate may be installed between thesetransparent electrodes and a polarizing plate, while preparing thepolarizing plate on the surface side of the transparent electrode.

Since the retardation plate and the polarizing plate have functionpolarizing the light that has entered as incident light from outside andhas been reflected by the metal electrode, they have an effect of makingthe mirror surface of metal electrode not visible from outside by thepolarization action. If a retardation plate is configured with a quarterwavelength plate and the angle between the two polarization directionsof the polarizing plate and the retardation plate is adjusted to π/4,the mirror surface of the metal electrode may be completely covered.

This means that only linearly polarized light component of the externallight that enters as incident light into this organic EL display istransmitted with the work of polarizing plate. This linearly polarizedlight generally gives an elliptically polarized light by the retardationplate, and especially the retardation plate is a quarter wavelengthplate, and moreover when the angle between the two polarizationdirections of the polarizing plate and the retardation plate is adjustedto π/4, it gives a circularly polarized light.

This circularly polarized light is transmitted through the transparentsubstrate, the transparent electrode and the organic thin film, and isreflected by the metal electrode, and then is transmitted through theorganic thin film, the transparent electrode and the transparentsubstrate again, and is turned into a linearly polarized light againwith the retardation plate. And since this linearly polarized light liesat right angles to the polarization direction of the polarizing plate,it cannot be transmitted through the polarizing plate. As the result,mirror surface of the metal electrode may be completely covered.

EXAMPLES

Description will be given of examples and others showing the compositionand effect of the invention in a concrete manner below. Note that a partor parts and % stated in the examples means a part by weight or parts byweight, and wt % unless otherwise specified.

Example 1

(Polarizer)

A polyvinyl alcohol film having a thickness of 75 μm, an averagepolymerization degree of 2400 and a saponification degree of 99.9 mol %was immersed in warm water of 30° C. for 60 sec and swollen. Then, theswollen film was further immersed in an aqueous solution of iodine andpotassium iodide (at a ratio of iodine to potassium iodide=0.5 to 8 inweight) at a concentration of 0.3% and thereby dyed while beingstretched by 3.5 times. Thereafter, the film was further stretched in aboric acid ester aqueous solution at 65° C. to a total stretch ratio of6. After the second stretching, the stretched film was dried in an ovenat 40° C. for 3 min to obtain a polarizer.

(Transparent Protective Film)

A triacetyl cellulose film having a thickness of 80 μm was used.

Example 1

(Preparation of Adhesive)

Dissolved into pure water in a temperature condition of 30° C. are 100parts of a polyvinyl alcohol-based resin having an acetoacetyl group(with an average polymerization degree of 1200, a saponification degreeof 98.5 mol % and an acetoacetylation degree of 5 mol %) and 32 parts ofmethylolmelamine to prepare an aqueous solution adjusted to have 4% ofthe solid matter concentation.

(Fabrication of Polarizing Plate)

The adhesive was coated on one surface of the transparent protectivefilm to form an adhesive layer having a thickness of 80 nm after drying.The coating of the adhesive was performed in a temperature condition of30° C. when 30 min elapsed after preparation of the adhesive. Triacetylcellulose films coated with the adhesive were adhered onto both surfacesof the polarizer at a temperature condition of 30° C. with a rolllaminator and thereafter, the polarizer with triacetyl cellulose filmsare dried at 55° C. for 6 min to thereby fabricate a polarizing plate.

Example 2

(Preparation of Adhesive)

Dissolved into pure water in a temperature condition of 30° C. are 100parts of a polyvinyl alcohol-based resin having an acetoacetyl group(with an average polymerization degree of 1200, a saponification degreeof 98.5 mol % and an acetoacetylation degree of 5 mol %) and 36 parts ofmethylolmelamine to prepare an aqueous solution adjusted to have 4% ofthe solid matter concentration.

(Fabrication of Polarizing Plate)

The adhesive was coated on one surface of the transparent protectivefilm to form an adhesive layer having a thickness of 90 nm after drying.The coating of the adhesive was performed in a temperature condition of30° C. when 30 min elapsed after preparation of the adhesive. Triacetylcellulose films coated with the adhesive were adhered onto both surfacesof the polarizer at a temperature condition of 30° C. with a rolllaminator and thereafter, the polarizer with triacetyl cellulose filmsare dried at 55° C. for 6 min to thereby fabricate a polarizing plate.

Example 3

(Preparation of Adhesive)

Dissolved into pure water in a temperature condition of 40° C. are 100parts of a polyvinyl alcohol-based resin having an acetoacetyl group(with an average polymerization degree of 1200, a saponification degreeof 98.5 mol % and an acetoacetylation degree of 5 mol %) and 43 parts ofmethylolmelamine to prepare an aqueous solution adjusted to have 4% ofthe solid matter concentration.

(Fabrication of Polarizing Plate)

The adhesive was coated on one surface of the transparent protectivefilm to form an adhesive layer having a thickness of 50 nm after drying.The coating of the adhesive was performed in a temperature condition of40° C. when 30 min elapsed after preparation of the adhesive. Triacetylcellulose films coated with the adhesive were adhered onto both surfacesof the polarizer at a temperature condition of 40° C. with a rolllaminator and thereafter, the polarizer with triacetyl cellulose filmsare dried at 55° C. for 6 min to thereby fabricate a polarizing plate.

Example 4

(Preparation of Adhesive)

Dissolved into pure water in a temperature condition of 30° C. are 100parts of a polyvinyl alcohol-based resin having an acetoacetyl group(with an average polymerization degree of 1200, a saponification degreeof 98.5 mol % and an acetoacetylation degree of 5 mol %) and 38 parts ofglyoxal to prepare an aqueous solution adjusted to have 4% of the solidmatter concentration.

(Fabrication of Polarizing Plate)

The adhesive was coated on one surface of the transparent protectivefilm to form an adhesive layer having a thickness of 90 nm after drying.The coating of the adhesive was performed in a temperature condition of30° C. when 30 min elapsed after preparation of the adhesive. Triacetylcellulose films coated with the adhesive were adhered onto both surfacesof the polarizer at a temperature condition of 30° C. with a rolllaminator and thereafter, the polarizer with triacetyl cellulose filmsare dried at 55° C. for 6 min to thereby fabricate a polarizing plate.

Example 5

(Preparation of Adhesive)

Dissolved into pure water in a temperature condition of 30° C. are 100parts of a polyvinyl alcohol-based resin having an acetoacetyl group(with an average polymerization degree of 1200, a saponification degreeof 98.5 mol % and an acetoacetylation degree of 5 mol %) and 32 parts ofmethylolmelamine to prepare an aqueous solution adjusted to have 10% ofthe solid matter concentration.

(Fabrication of Polarizing Plate)

The adhesive was coated on one surface of the transparent protectivefilm to form an adhesive layer having a thickness of 310 nm afterdrying. The coating of the adhesive was performed in a temperaturecondition of 30° C. when 30 min elapsed after preparation of theadhesive. Triacetyl cellulose films coated with the adhesive wereadhered onto both surfaces of the polarizer at a temperature conditionof 30° C. with a roll laminator and thereafter, the polarizer withtriacetyl cellulose films are dried at 55° C. for 6 min to therebyfabricate a polarizing plate.

Comparative Example 1

(Preparation of Adhesive)

Dissolved into pure water in a temperature condition of 23° C. are 100parts of a polyvinyl alcohol-based resin having an acetoacetyl group(with an average polymerization degree of 1200, a saponification degreeof 98.5 mol % and an acetoacetylation degree of 5 mol %) and 23 parts ofmethylolmelamine to prepare an aqueous solution adjusted to have 4% ofthe solid matter concentration.

(Fabrication of Polarizing Plate)

The adhesive was coated on one surface of the transparent protectivefilm to form an adhesive layer having a thickness of 100 nm afterdrying. The coating of the adhesive was performed in a temperaturecondition of 23° C. when 30 min elapsed after preparation of theadhesive. Triacetyl cellulose films coated with the adhesive wereadhered onto both surfaces of the polarizer at a temperature conditionof 23° C. with a roll laminator and thereafter, the polarizer withtriacetyl cellulose films are dried at 55° C. for 6 min to therebyfabricate a polarizing plate.

Comparative Example 2

(Preparation of Adhesive)

Dissolved into pure water in a temperature condition of 23° C. are 100parts of a polyvinyl alcohol-based resin having an acetoacetyl group(with an average polymerization degree of 1200, a saponification degreeof 98.5 mol % and an acetoacetylation degree of 5 mol %) and 48 parts ofmethylolmelamine to prepare an aqueous solution adjusted to have 4% ofthe solid matter concentration.

(Fabrication of Polarizing Plate)

The adhesive was coated on one surface of the transparent protectivefilm to form an adhesive layer having a thickness of 80 nm after drying.The coating of the adhesive was performed in a temperature condition of23° C. when 30 min elapsed after preparation of the adhesive, but notfabricate a polarizing plate because of a gelation of the adhesiveduring coating.

Comparative Example 3

(Preparation of Adhesive)

Dissolved into pure water in a temperature condition of 23° C. are 100parts of a polyvinyl alcohol-based resin having an acetoacetyl group(with an average polymerization degree of 1700, a saponification degreeof 88.5 mol % and an acetoacetylation degree of 6 mol %) and 10 parts ofhexamethylene diamine to prepare an aqueous solution adjusted to have 4%of the solid matter concentration.

(Fabrication of Polarizing Plate)

The adhesive was coated on one surface of the transparent protectivefilm to form an adhesive layer having a thickness of 120 nm afterdrying. The coating of the adhesive was performed in a temperaturecondition of 23° C. when 30 min elapsed after preparation of theadhesive. Triacetyl cellulose films coated with the adhesive wereadhered onto both surfaces of the polarizer at a temperature conditionof 23° C. with a roll laminator and thereafter, the polarizer withtriacetyl cellulose films are dried at 50° C. for 5 min to therebyfabricate a polarizing plate.

Comparative Example 4

(Preparation of Adhesive)

Dissolved into pure water in a temperature condition of 23° C. are 100parts of a polyvinyl alcohol-based resin having an acetoacetyl group(with an average polymerization degree of 1200, a saponification degreeof 98.5 mol % and an acetoacetylation degree of 5 mol %) and 15 parts ofglyoxal to prepare an aqueous solution adjusted to have 4% of the solidmatter concentration.

(Fabrication of Polarizing Plate)

The adhesive was coated on one surface of the transparent protectivefilm to form an adhesive layer having a thickness of 100 nm afterdrying. The coating of the adhesive was performed in a temperaturecondition of 23° C. when 30 min elapsed after preparation of theadhesive. Triacetyl cellulose films coated with the adhesive wereadhered onto both surfaces of the polarizer at a temperature conditionof 23° C. with a roll laminator and thereafter, the polarizer withtriacetyl cellulose films are dried at 50° C. for 5 min to therebyfabricate a polarizing plate.

(Evaluation)

The following kinds of evaluation were performed on the polarizingplates obtained in Examples 1 to 5 and in Comparative Examples 1, 3 and4.

(Peeling Length)

A sample was prepared by cutting a polarizing plate to obtain a piecehaving dimensions of 50 mm in the absorption axis direction of thepolarizer and 25 mm in a direction perpendicular to the absorption axisthereof. The sample was immersed in warm water of 60° C. and a peelinglength (mm) at an end portion of the sample was measured with thepassage of time.

Measurement of a peeling length (mm) was performed with a verniercaliper. Peeling lengths with time are shown in Table 1. Peeling lengths(mm) at the passage of 5 hr are shown in Table 2. TABLE 1 Test times(min) 0 50 100 150 200 250 300 350 400 450 500 550 600 Peeling lengths(mm) Example 1 0 0 0 0 0 0 0 0 0.25 0.25 0.25 0.25 0.25 Example 2 0 0 00 0 0 0 0 0 0 0 0 0 Example 3 0 0 0 0 0 0 0 0 0 0 0 0 0 Example 4 0 0 00 0 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 Example 5 0 0 0 0 0 0 0 0 00 0 0 0 Comparative 0 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5Example 1 Comparative 0 0.3 0.3 0.5 0.5 0.75 0.75 0.75 0.75 0.75 0.750.75 0.75 Example 3 Comparative 0 0.5 0.75 5 25 25 25 25 25 25 25 25 25Example 4(Decolorization of Iodine)

Decolorization of iodine in a polarizer was confirmed with the followingdecolorization evaluation method. That is, a sample was cut off from afabricated polarizing plate in the central portion in the widthdirection to obtain a piece in a way such that a size thereof is 50mm×25 mm and a long side thereof forms an angle of 45 degrees relativeto the absorption axis of the polarizing plate, and a singletransmittance (%) was measured with an integrating sphere transmittancemeasuring instrument (a trade name of DOT-3C, manufactured by MURAKAMICOLOR RESERCH LABORATORY). Another sample was, in a similar manner, cutoff from the polarizing plate after immersion in water for 3 hr and asingle transmittance (%) was measured on the sample to thereby obtain adifference therebetween (|ΔT % |).

(Appearance Evaluation)

A sample was prepared by cutting off from a polarizing plate to obtain apiece in a way such that a size thereof is 100 mm×100 mm. The sample isilluminated with light from a fluorescent lamp and appearance evaluationwas visually performed with respect to the presence or absence ofin-plane non-uniformity with reflection of light from the fluorescentlamp using the following criteria of “with non-uniformity” indicated bysymbol ◯ and “without non-uniformity” indicated by symbol ×,respectively. TABLE 2 Times elapsing till coating with Thicknessadhesive Decolorization Crosslinking agents of after of iodine: MixingControl adhesive preparation Peeling lengths changes in contenttemperature layers thereof when 5 hr single Appearance Kinds (parts) (°C.) (nm) (min) elapses (mm) transmittance evaluation Example 1 Methylol32 30 80 30 0 0.425 ∘ melamine Example 2 Methylol 36 30 90 30 0 0.371 ∘melamine Example 3 Methylol 43 40 50 30 0 0.217 ∘ melamine Example 4Glyoxal 38 30 90 30 0.25 0.633 ∘ Example 5 Methylol 32 30 310 30 0 0.302x melamine Comparative Methylol 23 23 100 30 0.5 0.842 ∘ Example 1melamine Comparative Methylol 48 23 80 30 — — — Example 2 melamineComparative Hexamethylene 10 23 120 30 0.7 1.380 ∘ Example 3 diamineComparative Glyoxal 15 23 100 30 25 0.993 ∘ Example 4

It is found from Table 2 that the polarizers of the examples experiencedabsolutely no peeling even in the condition of being immersed in warmwater, changes in single transmittance values of 0.7 or less withextremely low decolorization of iodine and excellency in moistureresistance. No problem occurs in appearance evaluation in Examples 1 to4.

INDUSTRIAL APPLICABILITY

A polarizing plate using an adhesive for polarizing plate of theinvention alone or an optical film obtained by laminating the polarizingplates can be preferably used in an image display such as a liquidcrystal display, an organic EL display or PDP.

1. An adhesive for polarizing plate used in order to provide atransparent protective film on at least one surface of a polarizer,comprising a crosslinking agent in the range of more than 30 parts byweight and 46 parts by weight or less relative to 100 parts by weight ofa polyvinyl alcohol-based resin having an acetoacetyl group.
 2. Theadhesive for polarizing plate according to claim 1, wherein thecrosslinking agent comprises glyoxal and/or a compound having a methylolgroup.
 3. The adhesive for polarizing plate according to claim 1,wherein the polarizer is a polyvinyl alcohol-based polarizer and thetransparent protective film is a cellulose-based transparent protectivefilm.
 4. A polarizing plate in which a transparent protective film isprovided on at least one surface of a polarizer with an adhesive layer,wherein the adhesive layer is formed with an adhesive for polarizingplate according to claim
 1. 5. The polarizing plate according to claim4, wherein a thickness of the adhesive layer is from 1 to 1000 nm.
 6. Afabrication method for polarizing plate in which a transparentprotective film is provided on at least one surface of a polarizer withan adhesive layer, comprising the steps of: preparing the adhesive forpolarizing plate according to claim 1; coating the adhesive forpolarizing plate on a surface of the polarizer on which the adhesivelayer is formed and/or a surface of the transparent protective film onwhich the adhesive layer is formed; and adhering the transparentprotective film and the polarizer.
 7. The fabrication method forpolarizing plate according to claim 6, wherein a time taken until theadhesive for polarizing plate is coated after the adhesive for polarizeris prepared is 240 min or less.
 8. The fabrication method for polarizingplate according to claim 6, wherein the preparation step for theadhesive for polarizing plate, the coating step for the adhesive forpolarizing plate and the adhesion step of adhering the transparentprotective film and the polarizer are all conducted at a temperature inthe state of from 25 to 50° C.
 9. An optical film comprising at leastone polarizing plate according to claim
 4. 10. An image displaycomprising a polarizing plate according to claim
 4. 11. An image displaycomprising the optical film according to claim 9.